1. Field of the Invention
The present invention relates to an automotive alternator having centrifugal fans for mounting on an automobile engine, and in particular relates to the construction of a voltage regulator case capable of effectively cooling a voltage regulator.
2. Description of the Related Art
FIG. 8 is a cross-section of the construction of a conventional automotive alternator.
Such a conventional automotive alternator comprises: a Lundell-type rotor 7 mounted so as to be freely rotatable by means of a shaft 6 within a case 3 comprising a front bracket 1 and a rear bracket 2 which are made of alminium; and a stator 8 secured to inner wall of the case 3 so as to cover the outer peripery of the rotor 7.
The shaft 6 is rotatably supported by the front bracket 1 and the rear bracket 2. A pulley 4 is secured to one end of the shaft 6 to enable rotational torque from an engine to be transmitted to the shaft 6 by means of a belt (not shown).
Slip rings 9 for supplying electric current to the rotor 7 are secured to the other end of the shaft 6, and a pair of brushes 10 are housed in a brush holder portion 11 disposed within the case 3 so as to slide in contact with the slip rings 9. A voltage regulator 18 for regulating an output voltage of the stator 8 is adhered to a heat sink 17 fitted to the brush holder portion 11. A rectifier 12 electrically connected to the stator 8 for rectifying an alternating current generated in the coil of the stator 8 to a direct current is mounted within the case 3.
The rotor 7 comprises a rotor coil 13 for generating a magnetic flux when an electric current flows therein and a pair of pole cores 14 disposed so as to cover the rotor coil 13 in which magnetic poles are formed by the magnetic flux generated by the rotor coil 13. The pair of pole cores 14 are secured to the shaft 6 facing each other so that claw portions intermesh. In addition, centrifugal fans 5 are secured to both ends of the rotor 7 in the axial direction.
The stator 8 comprises a stator core 15 and a stator coil 16 composed of wires wound around the stator core 15 in which an alternating current is generated by changes in the magnetic flux from the rotor 7 as the rotor 7 rotates.
Next, the mounted construction of the voltage regulator 18 will be explained with reference to FIGS. 9 and 10.
A voltage regulator case 25 is molded from insulating resin, and the brush holder portion 11, an annular shaft receiving portion 19, a circuit housing portion 22, a connector portion 23 and a condenser housing portion 24 are molded integrally therewith. Inserted conductors are insert-molded into the case 25. The inserted conductors constitute wiring paths between each of the elements mounted in the case 25, as well as projecting into the connector portion 23 to form connecting terminals 23a, and are exposed where necessary to form connecting terminals 34, etc., for electric connection to the rectifier 12.
The brush holder portion 11 is formed in the case 25 so that the shaft receiving portion 19 communicates with peripheral opening portions 11a, and brushes 10 are housed within the brush holder portion 11 such that one end of each of the brushes 10 projects into the shaft receiving portion 19. Moreover, springs (not shown) are disposed within the brush holder portion 11 and push the brushes 10 in the direction of projection. Caps 26 are mounted so as to block the other end of the peripheral opening portions 11a of the brush holder portion 11.
A board 21 mounted with electronic components such as integrated circuits, etc., constituting the voltage regulator 18 is secured by adhesive to the heat sink 17. The heat sink 17 is disposed with the circuit housing portion 22 so as to position the board 21 within the circuit housing portion 22, and a seal is formed between the heat sink 17 and edge portions of the circuit housing portion 22. Thereafter, lead pins 28 soldered to the board 21 are electrically connected to terminals exposed in the case 25, and sealing resin is injected into and hardened in the circuit housing portion 22.
The connecting terminals 23a projecting into the connector portion 23 comprise terminals for detecting battery voltage, terminals for alerting the driver of the vehicle to overvoltage or absence of power generation from the alternator, etc.
The condenser 29 suppresses surges generated as the voltage regulator 18 regulates the voltage, thereby preventing the propagation of noise in audio systems, etc., and is housed in the condenser housing portion 24.
Now, the voltage regulator case 25 is formed in an approximate fan shape centered on the annular shaft receiving portion 19 with the connector portion 23, the circuit housing portion 22, and the condenser housing portion 24 being arranged circumferentially, and the brush holder portion 11 is formed integrally on the front side of the circuit housing portion 22. The longitudinal direction of the cooling fins of the heat sink 17 (the longitudinal direction of the cooling fin located in the center) points towards the center of the shaft receiving portion 19, so that the longitudinal direction of the cooling fins of the heat sink 17 is parallel to the longitudinal direction of the condenser 29 and the longitudinal direction of the cooling fins of the heat sink 17 intersects the direction of projection of the connecting terminals 23a (the axial direction of the connector portion 23) at a right angle.
As shown in FIG. 11, the voltage regulator case 25 constructed in this manner is assembled by inserting the shaft 6 (not shown) into the shaft receiving portion 19 such that both ends of the voltage regulator case 25 in the circumferential direction fit together with both ends of the rectifier 12 in the circumferential direction. Thus, the voltage regulator case 25 and the rectifier 12 are disposed in a circle so as to surround the shaft 6. The caps 26 are formed such that the outside diameter thereof approximately coincides with the outermost diameter 30c of the centrifugal fans 5 and blocks the unused space portion 30d indicated by oblique lines in FIG. 11, so that the cooling air sucked from intake openings 1a caused by the rotation of the centrifugal fans 5 flows to the inner circumferential side along the surface of the voltage regulator case 25.
Now, the rectifier 12 comprises a pair of arc-shaped heat sinks 31a, 31b each having positive and negative diodes 32a, 32b plurally mounted on the main surface thereof and an arc-shaped circuit board 33 composed of conductors insert-molded into insulating resin. The rectifier 12 is formed in an arc shape by arranging the pair of heat sinks 32a, 32b coaxially with their main surfaces lying approximately in a same plane and arranging the circuit board 33 on the main surfaces of the pair of heat sinks 32a, 32b. The conductors constitute wiring paths between the diodes 32a, 32b, as well as being exposed where necessary to form connecting terminals 33a for electric connection to the connecting terminals 34 of the voltage regulator case 25.
In a conventional automotive alternator constructed in this manner, a current is supplied from a battery (not shown) by means of the brushes 10 and the slip rings 9 to the rotor coil 13, and a magnetic flux is generated. The claw portions of one pole core 14 are magnetized to N polarities by the magnetic flux, and the claw portions of the other pole core 14 are magnetized to S polarities. At the same time, the rotational torque of the engine is transmitted to the shaft 6 by means of the belt and the pulley 4, and the rotor 7 is rotated. Thus, a rotating magnetic field is imparted to the stator coil 16 and electromotive force is generated in the stator coil 16. This alternating electromotive force is rectified to a direct current by means of the rectifier 12, its voltage is regulated by the voltage regulator 18, and the battery is recharged.
The centrifugal fans 5 rotate so that the cooling air is sucked from intake openings 1a, 2a in the front bracket 1 and the rear bracket 2 and discharged to the outside through exhaust openings 1b, 2b. At that time, the cooling air sucked from the intake openings 2a in the rear bracket 2 flows radially inwards along the surface of the cooling fins of the heat sink 17 of the voltage regulator case 25 and the heat sink 31a of the rectifier 12, passes between the shaft 6 and the voltage regulator case 25 and between the shaft 6 and the rectifier 12, and is discharged thereafter through the exhaust openings 2b.
In a conventional automotive alternator constructed in this manner, the longitudinal direction of the condenser 29 is parallel to the longitudinal direction of the cooling fins of the heat sink 17 and the direction of projection of the connecting terminals 23a intersects the longitudinal direction of the cooling fins of the heat sink 17 at a right angle.
Thus, one problem is that the condenser housing portion 24 and the connector portion 23 inhibit the flow of the cooling air caused by the rotation of the centrifugal fans 5 as it moves radially inwards towards the inner circumference, increasing wind resistance to the cooling air flowing along the surface of the cooling fins of the heat sink 17, and therefore the voltage regulator 18 cannot be effectively cooled.
Another problem is that, as shown in FIG. 11, the circumferential angle 30a of the voltage regulator case 25 centered on the axis of the shaft 6 is greater than 180 degrees. In other words, the circumferential angle of the rectifier 12 is less than 180 degrees, making the surface area of the heat sink 31a insufficient for cooling and also making the spaces between the diodes 32a too narrow, and therefore the diodes 32a cannot be effectively cooled.
Yet another problem is that, as shown in FIG. 11, a corner portion 30e of the connector portion 23 projects radially outside the outermost diameter 30c of the centrifugal fans 5, requiring to form a recess portion for housing the corner portion 30e in the rear bracket 2. For that reason, the portion of the rear bracket 2 around the outside of the outermost diameter 30c of the centrifugal fans 5 cannot be formed in a circular shape, reducing mountability onto the automobile.